If something goes wrong with an initiative, the first thing a community manager should do is to cover for the authors of the initiative and other volunteers who have participated in it.
Some users feel a sense of fear of making an error and are afraid of situations where they potentially can be publicly criticized. This holds the users from becoming volunteers and prevents users from revealing their talents. If users can sense even the slightest confirmation of their fears, it will be very difficult for you to persuade them to become volunteers. Whatever happens, always support existing volunteers, cover them publicly and support them in private conversations. Volunteers should never experience any negative emotions or feelings of guilt if initiatives they participate in fail.
One effective approach to accomplish this is to create such a culture in which mistakes are encouraged. The thing that might help is facilitating public discussions of situations where something went wrong, without mentioning specific users, with further proposals for improving the initiative.
This is a fragment of a draft of the book “Lessons Learned While Working On Stack Overflow”. Read the full book on kindle or the paperback version.